A. James Clark School of Engineering

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    Fabrication of Bragg Gratings Using Interferometric Lithography
    (2007-04-30) Pizarro, Ricardo Andres; Goldhar, Julius; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A setup has been designed and realized for the fabrication of Bragg Gratings in edge emitting semiconductor laser. In this setup a HeCd laser, at 325nm, is used in a Lloyd's mirror configuration, to interferometrically expose a sinusoidal grating on photoresist. The dilution of photo-resistant (PR) material allows for a spincoat thickness of 50nm which is needed to minimize standing waves in the photo-resist that lead to a nonuniform exposure. Variations of exposure time show the progression of photo-resist gratings. Etching recipes using both dry and wet etching techniques were successfully used to transfer the grating pattern into semiconductor material. Bragg Gratings with period of 250nm in InP and InGaAs have been characterized with an Atomic Force Microscope to have a grating height of over 100nm.
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    DETERMINATION OF ROUND EXIT VELOCITY USING FIBER BRAGG GRATING SENSORS
    (2004-04-27) Aiyar, Arvind Ramaswamy; Davis, Christopher C; Electrical Engineering
    Optical fiber sensing technology has found widespread applications in smart structures and intelligent engineering systems. In particular, the use of fiber Bragg grating sensors for strain, temperature and pressure measurement has been an area of active research in the past decade. In this thesis, an experimental technique to measure the exit velocity of projectiles in field-deployed gun barrels is presented. In-fiber Bragg grating sensors are used to monitor the onset of propagating hoop strain waves accompanying the passage of rapidly moving projectiles. A fixed optical filter is used for providing temperature compensation and enable high-speed data acquisition. The elapsed time information extracted from the resulting strain waves is used to estimate the round exit velocity (REV). An approach based on short-time Fourier analysis and cross-correlation has been developed to accurately measure the REV to within 1% error. Results from live-fire tests are presented and compared to reference velocity data.